The instant invention is particularly designed as an improvement over U.S. Pat. No. 3,762,680, conveyed to the same assignee as the instant application. The "Background of the Invention" portion of U.S. Pat. No. 3,762,680 provides a detailed description of the state-of-the-art, from the use of heavy cast iron hot tops, to the more recent practice involving the use of improved "consumable" hot tops.
While consumable hot tops have certain advantages, including the ability to minimize piping, it has been found to be difficult to maintain them in position on top of the mold without having molten metal leak out at the interface between the hot top and the mold, or experiencing "floating", i.e., having the hot top rise from the top of the mold due to buoyancy, of the molten metal. Either of such occurences can result in ruining the ingot being poured. Furthermore, in instances where a sealing mechanism is provided between the consumable hot top and the mold, an additional problem can arise from the fact that as the cooling ingot shrinks, the contracting metal tends to adhere to the sealing mechanism, causing "hanger cracks" which can destroy a considerable portion of the ingot's outer surface.
The system taught in prior U.S. Pat. No. 3,762,680 attempts to overcome the drawbacks of other hot top sealing systems through the use of a bar device, basically a piece of steel associated with the consumable hot top, the bar being constructed to facilitate formation of a seal between the ingot mold and the hot top. Such a design has inherent drawbacks, however, in that the bar and its associated assembly is positioned inside the ingot mold. Consequently, a significant portion of the hot top is located in the interior of the mold, reducing the total size and volume of the ingot that can be cast. In addition, it has been found that as the ingot cools and its outer skin shrinks in a downward direction in the mold, the release of the ingot's skin from the bar does not consistently occur, many times causing cracks to develop in the skin, damaging the surface of the ingot.